ABSTRACT In the twenty years since effective HIV treatments became available, the lifespan of HIV-infected adults in high- resource settings has increased to within a decade of uninfected individuals. Nevertheless, antiretroviral treatments (ART) fall short in restoring health, and if therapy is discontinued virus usually rebounds to pretreatment levels due the persistence and reactivation of proviruses. Curative therapies are being sought, including therapeutic vaccines, chemotherapies paired with stem-cell transplant, chimeric antigen receptor T cells, neutralizing and immune modulating antibodies, gene therapies, cytokines and initiation of ART during acute infection. While some of these approaches have reduced the ?reservoirs? of infectious viruses and in one case may have cured HIV infection, a better understanding of the mechanisms underlying HIV persistence is needed to develop an effective, safe and economical cure. HIV reservoirs are primarily established early in infection, and while they decay and change in composition during ART, the mechanisms that sustain reservoirs are only partially known. We hypothesize that HIV reservoirs are maintained by: (1) Integrated proviruses that modulate gene expression to promote survival of these cells, allowing infected cells to persist by proliferation or latency; (2) HIV-specific immune responses become exhausted due to dysregulation of T-regulatory cells resulting from provirus integration; and (3) Epigenetic marks repress expression of proviral DNA, allowing infected cells to persist due to ?deep? latency of proviruses. We propose studies to explore the role of these mechanisms in sustaining HIV reservoirs using specimens collected prospectively from a unique Belgian cohort of chronically infected individuals sampled during ART-suppression as well as during and after an analytical treatment interruption (ATI). Samples for this study include blood, cerebral spinal fluid, bone marrow, bronchioalveolar lavage fluid, lymph node, duodenum, ileum, and colon. The knowledge gained from the proposed studies should point to interventional strategies that could be tested and potentially contribute to the goal of developing an intervention to cure HIV infection.